Coke Drum ID Cracking

[reesecc66]

I just recently got a job as a Reliability Engineer in the refinery and have been hired at our Coker unit. We have just started turnaround and are seeing some unexpected things on the inside. This is the second turnaround for this unit.

Our drums are 2" ASME SA387 Gr. 22 CL2 with 1/8" 405SS roll bonded cladding. The circumferential welds have an INCO 82 weld restoration. We run 16 hour cycles.

Repairs that were gone after at the last TA were bulges and cracking at what we call the Tri Metal Junction, where the 387, 405, and 82 all meet.

Bulge repairs were made by stripping back the 405 and welding either 2 or 3 passes of INCO 625 for strengthening. These were approximately 14 - 15" high about the center of the bulge. This did not tie back into the 405.

Cracking at circumferential weld seams were repaired by removing the INCO 82 restoration and WBU with E7018-B2L.

PROBLEMS WE SEE NOW.
Cracking at majority of B2L WBU to 387 interface and cracking at 625 to 387 interface. We haven't seen much significant bulge growth from laser scans and our bare 387 looks good too.

What I am trying to decide is was the B2L a good selection for the circ. weld seam WBU or should something else have been used and should we stop making weld interfaces to the 387.

Thanks in advance for the help.

 

[Longinthetooth]

I dont know much about your metalurgy, but (when I was in the business) the main reason for coke drum bulges was filling with water too fast when you are quenching the off line drum. There was an empirical formula for how long it should take you to quench the drum. I've forgotten it now, but you should be able to find it on the web somewhere. We stuck to this rigidly and never had a bulge or any need for a repair in +20 years.